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WAEC 2017 · Paper 2 · Q7

A car travelling at 15 m s−115\text{ m s}^{-1} is brought to rest with uniform retardation in 5 seconds. Find the:

  1. (a)

    retardation;

  2. (b)

    distance travelled before coming to rest.

Worked solution (try it first)
  1. u=15u = 15, v=0v = 0 and t=5t = 5.

(a)

  1. v=u+atv = u + at: 0=15+5a0 = 15 + 5a, so a=−3a = -3: a retardation of 3 m s−23\text{ m s}^{-2}.

(b)

  1. s=12(u+v)ts = \frac12(u + v)t
    =12(15)(5)= \frac12(15)(5)
    =37.5 m= 37.5\text{ m}.

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